The invention relates generally to disc drives and more particularly to a lapped disc clamp used to secure a disc platter assembly to a spin motor, as well as, a process for manufacturing the lapped disc clamp and a disc clamp designed to more uniformly equalize the clamping force exerted on the disc.
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are typically coated with a magnetizable medium and mounted on the hub of a spin motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by transducers (xe2x80x9cheadsxe2x80x9d) mounted to an actuator assembly for movement of the heads relative to the discs. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment. Critical to both of these operations is the accurate locating of the head over the center of the desired track.
The heads are each mounted via flexures at the ends of actuator arms that project radially outward from the actuator body or xe2x80x9cExe2x80x9d block. The actuator body typically pivots about a shaft mounted to the disc drive housing adjacent the outer extreme of the discs. The pivot shaft is parallel to the axis of rotation of the spin motor and the discs, so that the heads move in a plane parallel to the surfaces of the discs.
Typically, such actuator assemblies employ a voice coil motor to position the heads with respect to the disc surfaces. The voice coil motor typically includes a flat coil mounted horizontally on the side of the actuator body opposite the actuator arms. The coil is immersed in a vertical magnetic field of a magnetic circuit comprising one or more permanent magnets and vertically spaced apart magnetically permeable pole pieces. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces. The actuator thus allows the head to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs.
Modern disc drives typically include one or more discs mounted to the spin motor. Spacers are used to provide the separation between discs necessary for the actuators arms to movably locate the heads in relation with the disc surfaces. The discs and spacers collectively form a disc stack assembly, or disc pack, that is mounted on the spin motor hub and held together with a leaf spring disc clamp.
Disc clamps can be either stamped or milled. While milled clamps are more rigid and less prone to deflecting the abutting disc surface, they are relatively expensive to produce. Consequently, stamped leaf spring disc clamps, which are substantially less expensive, have become popular. The clamp is typically a circular spring-steel, sheet metal structure having a central portion and a rib portion at or near the OD of the clamp, with an annular rib formed in the rim portion of the clamp. The central portion of the leaf spring disc clamp has a partial aperture that is bent or deflected toward the center of the clamp, forming a leaf spring above the level of the annular rib, and includes a plurality of screw holes spaced symmetrically about the central portion of the clamp. The screws used to mount the disc clamp springingly bend and deflect the central portion of the clamp toward the upper surface of the motor spindle as the screws are tightened, thereby forcing the annular rib into firm contact with the uppermost disc surface and applying a clamping force to the disc stack.
This type of disc clamp is not without problems. The disc clamp is secured with a plurality of screws, typically 3, circumferentially spaced around the center of the clamp. The majority of the clamping force is exerted by the rib portion adjacent the screw locations, with a somewhat reduced level of clamping force exerted by the rib portion between the screw locations. This variation in clamping force can mechanically distort the discs in a phenomenon sometimes referred to as xe2x80x9cpotato chipping,xe2x80x9d meaning that the portions of the disc nearest the clamp screws are displaced further than the portions of the disc between the screws.
One solution to xe2x80x9cpotato chippingxe2x80x9d is to increase the number of mounting screws used to secure the disc clamp to the spin motor hub. As more screws are used and are spaced closer together, the discrepancy in clamping force is reduced but not eliminated. A disadvantage of this approach is that the use of additional screws complicates the manufacturing and assembly process.
Mechanical distortion of the disc surface can, in turn, lead to undesirable variations in the read/write signals detected and written by the heads of the disc drive. Since the heads will fly at varying heights around the circumference of the disc while attempting to follow a distorted disc, the signals used to read and write data on the discs may be inadequate to ensure reliable data storage and recovery.
Against this backdrop the present invention has been developed. The performance of a leaf spring disc clamp can be enhanced by increasing the flatness of an annular contact surface in its fully deflected, installed position. Such a disc clamp exhibits a substantially improved flatness in the installed state at a minor expense in applied axial force and thus has a more uniform force distribution applied around the annular contact surface. It has further been determined that a lapping process can be used to achieve a desired level of performance without fully deflecting the clamp prior to installation in a disc pack.
Accordingly, an aspect of the invention is found in a method of manufacturing a leaf spring disc clamp for use in a disc drive to clamp a data storage disc to a spindle hub of a spin motor. The method includes the steps of forming a piece of spring sheet metal into a generally circular leaf spring disc clamp having an annular rim portion and a central bowed leaf spring portion. The clamp is then placed on a lapping surface, and a force is applied to the central portion of the clamp to partially deflect the central portion of the clamp from an undeflected position toward the lapping surface. The clamp is then moved relative to the lapping surface to abrade and remove a portion of the rim portion to form a flattened annular contact surface on the rim portion.
Another aspect of the invention is found in a leaf spring disc clamp for fastening a data disc to a disc spin motor hub in which an annular rim portion forms an annular rib that has a flat annular contact surface thereon for uniformly distributing clamping force onto the data disc.
Yet another aspect of the present invention involves providing one or more slots within the central portion of the disc clamp and joining the slots with a central aperture in the central portion in order to more uniformly distribute the clamping force around the annular rib of the disc clamp and thereby improve disc flatness during disc drive operation.
These and other features as well as advantages that characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.